Method and system for wireless communications between base and mobile stations

ABSTRACT

A method and system for wireless communications between base and mobile stations use reference signals transmitted from base stations prior transmission of data signals. The reference signals are used to determine propagation characteristics of communication channels between the base and mobile stations and optimize, in real time, parameters of receivers of the mobile stations for processing the following data signals. Applications of the invention include wireless communication systems compliant with OFDMA, 3GPP LTE, RFN-OFDMA, OFDM, TDMA, and the like communication protocols.

PRIORITY

This application is a continuation of and claims priority to co-ownedco-pending U.S. patent application Ser. No. 11/688,125 of the same titlefiled Mar. 19, 2007, the foregoing incorporated herein by reference inits entirety.

BACKGROUND

1. Field

The present inventions relates generally to the field of wirelesscommunications, and more specifically, to a method and system forwireless communications between base and mobile stations.

2. Related Art

In wireless communication system using communication protocols based ontime division multiplexing techniques (for example, an OrthogonalFrequency Division Multiple Access (OFDMA) communication protocol), abase station transmits information to a mobile station withpre-determined periodicity during pre-assigned time intervals. To reducepower consumption and extend battery life, between such time intervals areceiver of the mobile station is switched to an energy-saving standbystate.

However, during periods of time between consecutive transmissions,propagation characteristics of a communication channel between the baseand mobile stations may change significantly. As a result, whenre-activated, the receiver of the mobile station may not be optimallyconfigured for receiving transmissions from the base station.

Despite the considerable effort in the art devoted to development ofmethods and systems for communications between base and mobile stations,further improvements would be desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and is notlimited by the accompanying figures, in which like references indicatesimilar elements, except that suffixes may be added, when appropriate,to differentiate such elements. It is contemplated that features orsteps of one embodiment may beneficially be incorporated in otherembodiments without further recitation. Elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale.

FIG. 1 is a schematic diagram illustrating a portion of a system forwireless communications adapted for implementing an embodiment of thepresent invention.

FIG. 2 is a schematic timing diagram of reference and data signals usedin the system of FIG. 1.

FIG. 3 is a schematic diagram illustrating an exemplary allocation offrequencies of the reference and data signals of FIG. 2 in the frequencydomain.

FIG. 4 is a schematic diagram of an exemplary base station of the systemof FIG. 1 in accordance with one embodiment of the present invention.

FIG. 5 is a schematic diagram of an exemplary mobile station of thesystem of FIG. 1 in accordance with one embodiment of the presentinvention.

FIG. 6 is a flow diagram illustrating a method for transmittinginformation in the system of FIG. 1 in accordance with one embodiment ofthe present invention.

DETAILED DESCRIPTION

Referring to the figures, FIG. 1 depicts a schematic diagramillustrating a portion of a wireless communication system 100 adaptedfor implementing an embodiment of the present invention, and FIG. 2depicts a schematic timing diagram 200 of reference and data signalsused in the system 100 as a function of time (axis 201).

Generally, the system 100 is compliant with a communication protocolsuch as an Orthogonal Frequency Division Multiple Access (OFDMA)communication protocol, a Third Generation Partnership Project Long TermEvolution (3GPP LTE) communication protocol, a Random Frequency-HoppingOFDMA (RFN-OFDMA) communication protocol, an OrthogonalFrequency-Division Multiplexing (OFDM) communication protocol, or a timedivision multiple access (TDMA) communication protocol, among othercommunication protocols.

Illustratively, the system 100 comprises a plurality of base stations110 and a plurality of mobile stations (or units of user equipment (UE))120. The base stations 110 are communicatively selectively coupled toone another via interfaces 130 (for example, wireless (as shown), wired,or optical interfaces), and the mobile stations 120 are selectivelycoupled to the respective regional base stations 110 via wirelessinterfaces 140.

In the depicted embodiment, mobile stations 120 ₁-120 _(N) and 120_(N+1)-120 _(M) are coupled to the base stations 110 ₁ and 110 _(K),respectively, where N, M, and K are integers and M>N. In exemplaryapplications, a mobile station is wireless communication device such asa cellular phone, a personal digital assistant (FDA), a mobile computer,and the like.

Referring to FIG. 2, in operation, a base station 110 cyclicallytransmits to a particular mobile station 120, with a pre-determinedperiodicity 230, a reference signal 210 (denoted as “R”) and a datasignal 220 (denoted as “DATA”) carrying information directed to thatmobile station. In one embodiment, the data signal 220 constitutes asub-frame of a downlink in the context of the 3GPP LTE communicationprotocol.

In one embodiment, the reference signal is determined by (i) atime-frequency pattern of reference symbol locations and (ii) amplitudeand phase modulation of a sequence applied to the reference symbollocations. For example, the reference symbol locations may be separated,in, the time domain, approximately by integer multiples of 1/14milliseconds and, in the frequency domain, by multiples of 15 kHz.Typical sequences used to create the amplitude and phase modulationapplied to the reference symbol locations have near-zerocross-correlation and near-zero autocorrelation properties. Examples ofsuch sequences include the Generalized Chirp-Like (GCL) sequence, theConstant Amplitude Zero Auto-Correlation (CAZAC) sequence, and the Walshsequence.

In the time domain, the reference signal 210 precedes the respectivedata signal 220 (for example, a reference signal 210 _(L) precedes adata signal 220 _(L), where L is an integer). More specifically, thereference signal 210 and the data signal 220 are transmitted during timeintervals 202 and 212, respectively, which are separated by a timeinterval 204. In operation, after receiving the data signal 220(illustratively, at a moment T2), a receiver of the mobile station 120is switched from an active state to a standby state until a moment T1.The moment T1 precedes an arrival of the reference signal 210 of theconsecutive cycle 230 and, at the moment T1, the receiver of the mobilestation is switched back to the active state.

In one embodiment, the duration of the reference signal 210 is fromabout 20 to 200 μsec, the duration of the time interval 204 is fromabout 0.3 to 3 msec, the duration of the data signal 220 is from about0.5 to 5 msec, and the duration of the time interval 230 is from about0.5 to 5 see.

In operation, during a time interval 214 separating consecutivetransmissions of the data signals 220, propagation characteristics of acommunication channel between the base and mobile stations may changesubstantially enough to have detrimental effect of qualitativeparameters of the system 100. The reference signal 210 is generally atest signal having pre-determined characteristics that is transmitted tothe mobile station(s) for determining instant propagationcharacteristics of the communication channel. Using results of analysisof reception of the reference signal 210, the mobile station adjusts, inreal time, configuration parameters of its receiver to optimizereception of the data signal 220 shortly following the reference signal210 upon expiration of the time interval 204.

FIG. 3 depicts a schematic diagram 300 illustrating an exemplaryallocation of frequencies of the reference and data signals of FIG. 2 inthe frequency domain (x-axis 301). In the depicted embodiment, thereference signal 210 is illustratively transmitted at a sub-carrierfrequency 302, and the data signals 220 directed to respective mobilestations 120 are selectively transmitted at sub-carrier frequencies 304.The frequencies 302 and 304 generally are sub-carrier frequencies of thesystem 100 and disposed within bandwidths 310 of receivers of the mobilestations 120.

In the depicted embodiment, the reference signal 210 is transmitted at asub-carrier frequency disposed at a boundary of a bandwidth 310 andallocated at a spectral distance 306 from a particular sub-carrierfrequency 304. In alternate embodiments, any sub-carrier frequency 304may by used for transmitting the reference signal 210, as well as thesame sub-carrier frequency may used for transmitting both the referenceand data signals. Typically, carrier frequencies of the reference anddata signals 210, 220 are in a range from 400 MHz to 2.6 GHz,sub-carrier frequencies 302, 304 are on a 15 kHz raster over 1.25 MHz to20 MHz bandwidths offset by a respective carrier frequency, and thespectral distance 306 is an integer multiple of 15 kHz.

In further embodiments, in consecutive cycles 230, the reference anddata signals 210 and 220 may be transmitted at different sub-carrierfrequencies (for example, frequencies changed in pre-selected pattern).Additionally or alternatively, in the time domain, at least portions ofthe reference and data signals may also be transmitted using differentor multiple sub-carrier frequencies. As such, in various embodiments, inthe time/frequency continuum, the base station 110 may generate aplurality of the reference signals 210 having the same or differentfrequencies, where each reference signal precedes the respective datasignal 220, which is directed to a particular mobile station 120 andtransmitted at a single or multiple sub-carrier frequencies.

FIG. 4 depicts a schematic diagram of an exemplary base station 110 ofthe system 100 of FIG. 1 in accordance with one embodiment of thepresent invention. The base station 110 generally comprises an antenna402, a transmitter 410, a generator 412 of the reference signal 210, areceiver 420, a data processor 430, a program memory 440, timingcircuits 450, support systems 460, and interfaces (illustratively, shownas a common bus 404) supporting data/command exchanges betweencomponents of the base station.

Programs of a respective communication protocol implemented in thesystem 100 are stored in the program memory 440 and, when executed bythe data processor 430, facilitate operability of the base station 110.In particular, the transmitter 410 and receiver 420 supportbi-directional wireless communications between the base station 110 andadjacent base station(s) of the system 100 and between the base station110 and a plurality of the mobile stations 120. In operation, the timingcircuits 450 generate synchronization signals, which facilitateallocation of pre-determined time slots for uplink and downlinktransmissions to each of the mobile stations 120. Input/output devices,power sources, and the like auxiliary components of the base station 110are collectively denoted herein as support systems 460.

In the depicted embodiment, the generator 412 is shown as a stand-alonedevice coupled to the transmitter 410, however, in an alternateembodiment, the generator 412 may be a portion of the transmitter 410.Alternatively or additionally, at least portions of the generator 412may be implemented in software as a computer program stored in theprogram memory 440 and, in operation, executed by the data processor430. In yet another embodiment, the generator 412 may directly becoupled to the antenna 402.

FIG. 5 is a schematic diagram of an exemplary mobile station 120 of thesystem 100 of FIG. 1 in accordance with one embodiment of the presentinvention. The mobile station 120 generally comprises an antenna 502, atransmitter 510, a receiver 520, digital signal processing (DSP)circuits 530, a memory module 540, a processor 550, user interface 560,auxiliary devices collectively denoted herein as support circuits 570, abattery 580 powering components of the mobile station, and interfaces(illustratively, shown as a common bus 504) supporting data/commandexchanges between components of the mobile station.

In operation, the processor 550 administers operation of the mobilestation 120 by executing programs stored in the memory module 540 andfollowing user instructions entered via the user interface 560. The userinterface 560 may include at least some of a speaker, a microphone, adisplay, a keyboard, wired or optical connectors, pushbuttons, orindicators, among other devices adapted to facilitate human or machineinteractions with a computerized communication device such as mobilestation 120.

The DSP circuits 530 generally provide synchronization between thetransmitter 510 and receiver 520 and the base station 110, as well asfacilitate support for the user interface 560. Illustratively, the DSPcircuits 530 includes a timer 532 providing, in particular,synchronization between timing of transitions to active/standby statesof the transmitter 510 and the reference and data signals 210 and 220 ofthe base station 110, as discussed above in reference to FIG. 2. Inalternate embodiments, at least a portion of functions of the DSPcircuits 530 may be implemented in software as a computer program storedin the memory module 540 and, in operation, executed by the processor550.

Via the antenna 502, the transmitter 510 and receiver 520 supportbi-directional communications between the mobile station 120 and therespective base station 110. In one embodiment, the receiver 520includes a demodulator/amplifier 512, an analog-to-digital converter(ADC) 514, and a control module 516. In operation, the receiver 520receives and processes downlink transmissions from the base station 110,each such transmission comprising the reference and data signals 210 and220, as discussed above in reference to FIGS. 2-3.

After receiving the reference signal 210, the control module 516analyses a corresponding feedback signal forwarded to the module 516 viainterface 518. Based on results of the analysis, the control module 516determines propagation characteristics of a communication channelbetween the base and mobile stations and adjusts, in real time,configuration parameters of the demodulator/amplifier 512 to provideoptimal conditions for receiving the data signal 220. In one embodiment,the control module 516 adjusts at least one of a gain, a bandwidth, oran in-phase/quadrature compensation of the demodulator/amplifier 512,among other configuration parameters of the receiver 520.

In the depicted embodiment, the control module 516 is a stand-alonehardware portion of the receiver 520, whereas the feedback signal isprovided to the module 516, in a digital format, from the ADC 514. In analternate embodiment, the demodulator/amplifier 512 may be a source ofthe feedback signal provided in an analog format. In furtherembodiments, some or all portions of the control module 516 may beimplemented in software as a computer program stored in the memorymodule 540 and, in operation, executed by the processor 550.

FIG. 6 depicts a flow diagram illustrating a method 600 for transmittinginformation in the system 100 of FIG. 1 in accordance with oneembodiment of the present invention. In exemplary applications, themethod 600 is used to enhance performance and, in particular, Quality ofService (QoS) characteristics of the system 100, as well as reduce powerconsumption in the mobile stations 120.

For brevity, the method 600 is discussed herein in the context of asingle base station 110 and a single mobile station 120. Those skilledin the art will readily appreciate that the same method steps areperformed, during cyclically repeated time intervals each defined by therespective adjacent moments T1 (discussed in reference to FIG. 2), foreach mobile station 120 in communication with a particular base station110.

The method 600 starts at step 610, where, at the moment T1 preceding anarrival of the reference signal 210, the receiver 520 of the mobilestation 120 is switched from a standby state to an active state. In oneembodiment, the receiver 520 is initially assigned the configurationparameters used in a preceding active state, i.e., prior to switchingthe receiver to the standby state. Switching the receiver 520 to theactive state may be triggered, for example, by a signal generated usingthe timer 532 synchronized with the timing circuits 450 of the basestation 120.

At step 620, the base station 110 transmits and the mobile station 120receives the reference signal 210. An amplitude of the transmittedreference signal 220 is pre-selected to provide, within operating rangeof the base station 110, a high signal-to-noise ratio (SNR) of an outputsignal of the demodulator/amplifier 512 of the receiver 520 and,correspondingly, a high SNR of an output signal of the ADC 514. Thereference signal 210 is transmitted at one of sub-carrier frequenciesused in the system 100 and, in different transmissions, may betransmitted at different sub-carrier frequencies.

Using a feedback signal produced by the demodulator/amplifier 512 or theADC 514, the received reference signal 210 is analyzed using the controlmodule 516 of the receiver 520. An algorithm used by the control module516 to analyze the reference signal 210 may be implemented in a form ofhardware, software, or a combination thereof in the module 516 or atleast portions of the algorithm may be implemented in a form of acomputer program stored in the memory module 540 of the receiver 520. Inone embodiment, the algorithm is directed to determining parameters ofthe Rayleigh fading of the reference signal 210 in the communicationchannel between the base and mobile stations.

At step 630, using results of the analysis of the reference signal 210,the configuration characteristics (e.g., gain, bandwidth,in-phase/quadrature compensation, among other parameters) of thereceiver 520 are adjusted to provide optimal conditions (e.g., maximumSNR) during reception of the data signal 220. The receiver 520 havingthe adjusted configuration characteristics may use the ADC 514 havingreduced dynamic range and, consequently, low power consumption. In oneembodiment, the analysis of the reference signal 210 is completed andthe configuration characteristics are adjusted prior to expiration ofthe time interval 204.

In one embodiment, when propagation characteristics of the communicationchannel between the base and mobile stations momentarily deteriorate toa point that the reference signal is missed in the channel, the controlmodule 516 restores/maintains the configuration parameters definedduring at least one of most recent transmissions.

At step 640, the base station 110 transmits and the mobile station 120receives the data signal (i.e., sub-frame) 220. The data signal 220 istransmitted at one of the sub-carrier frequencies 404 that may either beequal to or different from the sub-carrier frequency of the referencesignal 210, as well as may hop during the transmission (i.e., duringtime interval 212) or differ from one transmission to another. Using thereceiver 520 having its configuration characteristics adjusted asdiscussed above in reference to steps 620 and 630, the mobile station120 provides, at minimal power consumption, reception of the data signal220 with a peak SNR.

At step 640, after receiving the data signal 220, at the moment T2, thereceiver 520 is switched from the active state to the energy-savingstandby state. A transition to the standby state may be initiated using,for example, a signal produced by the timer 532. To preserve resourcesof the battery 580, the receiver 520 is maintained in the standby stateuntil the moment T1 of the next transmission cycle 230, where the stepsof method 600 are repeated, as shown with a link 602.

In a further embodiment, the system 100 may be a Multiple-InputMultiple-Output (MIMO) wireless communication system using multipleantennas at the base and mobile stations and employing at least one ofbeamforming, spatial multiplexing, or diversity coding techniques.

In one example of a MIMO system, the antenna 402 of the base station 110would represent a composite antenna having multiple, specially separatedantenna structures. Each antenna structure is selectively adapted fortransmitting same or different signals at pre-selected pluralities ofsub-carrier frequencies. Correspondingly, in said MIMO embodiment, theantenna 502 of the mobile station 120 may also be a composite antennahaving multiple antenna units each selectively adapted for receivingparticular portions of signals transmitted by the base station 110. Inthis embodiment, the receiver 520 would be a multi-section unit, whereeach section includes the demodulator/amplifier 512, ADC 514, and acontrol module 516. Inputs and outputs of these sections are selectivelycoupled to particular antennas units of the composite antenna 502 and tothe common bus 504, respectively.

In operation, in such a MIMO system a plurality of communicationchannels is established, at multiple sub-carrier frequencies, betweenthe antenna structures of the base and the antenna units of the mobilestations, and the reference and data signals 210 and 220 are transmittedthrough these channels or pre-determined portions thereof. Using thereference signal 210, configuration parameters of each section of themulti-section receiver 520 are adjusted, prior to arrival of the datasignal 220, as discussed above in reference to FIG. 6.

As used herein, a software system can include one or more objects,agents, threads, subroutines, separate software applications, two ormore lines of code or other suitable software structures operating inone or more separate software applications, on one or more differentprocessors, or other suitable software architectures.

As will be appreciated, the processes in preferred embodiments of thepresent invention may be implemented using any combination of computerprogramming software, firmware or hardware. As a preparatory step topracticing the invention in software, the computer programming code(whether software or firmware) according to a preferred embodiment willtypically be stored in one or more machine readable storage mediums suchas fixed (hard) drives, diskettes, optical disks, magnetic tape,semiconductor memories such as read-only memories (ROMs), programmableROMs (PROMs), etc., thereby making an article of manufacture inaccordance with the invention. The article of manufacture containing thecomputer programming code is used by either executing the code directlyfrom the storage device, by copying the code from the storage deviceinto another storage device such as a hard disk, random access memory(RAM), etc., or by transmitting the code for remote execution. Themethod form of the invention may be practiced by combining one or moremachine-readable storage devices containing the code according to thepresent invention with appropriate standard computer hardware to executethe code contained therein. An apparatus for practicing the inventioncould be one or more computers and storage systems containing or havingnetwork access to computer program(s) coded in accordance with theinvention.

Unless stated otherwise, terms such as “first” and “second” are used toarbitrarily distinguish between the elements such terms describe. Thus,these terms are not necessarily intended to indicate temporal or otherprioritization of such elements. Also the invention is described hereinwith reference to specific embodiments, various modifications andchanges can be made without departing from the scope of the presentinvention. Accordingly, the specification and figures are to be regardedin an illustrative rather than a restrictive sense, and all suchmodifications are intended to be included within the scope of thepresent invention. Any benefits, advantages, or solutions to problemsthat are described herein with regard to specific embodiments are notintended to be construed as a critical, required, or essential featureor element of any or all the claims.

1. A method comprising: receiving a reference signal having one or morepredetermined characteristics; determining at least one propagationcharacteristic of a communication channel based at least in part on theone or more predetermined characteristics of the received referencesignal; adjusting one or more receiver configuration parameters of areceiver based on the determined at least one propagationcharacteristics of the communication channel; receiving a data signalusing the receiver having the adjusted configuration parameters; andwherein the reference signal immediately precedes the data signal. 2.The method of claim 1, further comprising activating the receiver from astandby state immediately prior to arrival of the reference signal. 3.The method of claim 2, wherein the receiver is activated from thestandby state according to a predefined schedule.
 4. The method of claim1, wherein the data signal is received on the same communicationchannel.
 5. The method of claim 1, wherein at least a portion of thedata signal is received on a different communication channel.
 6. Themethod of claim 1, wherein the reference signal is determined by (i) atime-frequency pattern of reference symbol locations and (ii) amplitudeand phase modulation of a sequence applied to the reference symbollocations.
 7. The method of claim 6, wherein the sequence is furtherselected from the group consisting of: (i) a Generalized Chirp-Like(GCL) sequence, (ii) a Constant Amplitude Zero Auto-Correlation (CAZAC)sequence, and (iii) a Walsh sequence.
 8. A device comprising: a wirelessreceiver having at least one adjustable configuration parameter; and aprocessor; and a computer readable medium comprising instructionsconfigured to when executed by the processor: receive a reference signalhaving one or more known characteristics; determine an instantpropagation characteristic of a communication channel based on thereceived reference signal only; adjust at least one configurationparameter of the wireless receiver based on the determined propagationcharacteristic of the communication channel; and receive a data signalusing the adjusted wireless receiver.
 9. The device of claim 8, furthercomprising a wireless transmitter.
 10. The device of claim 8, whereinthe computer readable medium further comprises instructions which whenexecuted by the processor activate the device from an inactive mode,based at least in part on a predefined schedule.
 11. The device of claim8, wherein the wireless receiver is configured to receive OrthogonalFrequency Division Multiplexed (OFDM) signals.
 12. The device of claim8, wherein the wireless receiver is configured to receive the referencesignal via at least one subcarrier.
 13. The device of claim 12, whereinthe wireless receiver is configured to receive the data signal via theat least one subcarrier.
 14. The device of claim 12, wherein thewireless receiver is configured to receive the data signal via at leastone different subcarrier.
 15. A base station, the base stationcomprising: an antenna; a transmitter coupled to the antenna and adaptedfor transmitting signals at a first plurality of sub-carrierfrequencies; a processor; and a computer readable medium comprisinginstructions configured to, when executed by the processor, transmit areference signal and a data signal to at least one mobile station of thesystem; wherein: the mobile station can determine an instant propagationcharacteristic of a communication channel based on the reference signalonly; and the mobile station can adjust its receiver based on thedetermined instant propagation characteristics of the communicationchannel to receive the data signal.
 16. The base station of claim 15,further adapted to generate the reference signal and the data signal atthe same sub-carrier frequency.
 17. The base station of claim 15,further adapted to generate at least portions of the reference signal orthe data signal at different or multiple sub-carrier frequencies. 18.The base station of claim 15, wherein the reference signal comprises:(i) a time-frequency pattern of reference symbol locations and (ii)amplitude and phase modulation of a sequence applied to the referencesymbol locations.
 19. The base station of claim 15, wherein thereference signal is selected from the group consisting of a GeneralizedChirp-Like (GCL) sequence, a Constant Amplitude Zero Auto-Correlation(CAZAC) sequence, and a Walsh sequence.
 20. The base station of claim15, wherein the at least one mobile station comprises a plurality ofmobile stations.
 21. The base station of claim 20, wherein each of theplurality of mobile stations has a corresponding reference signal.